Magnetic disk data storage systems generally include a rotating magnetic disk and a read/write head that reads and writes data along concentric tracks on the magnetic disk. Some read/write heads use a separate magnetoresistive read element for reading data and a thin film write element for writing data. The read element is optimized for reading data stored on the magnetic disk while the write element is optimized for storing data on the magnetic disk. This optimization often includes making the read element significantly narrower than the write element to avoid erroneously reading data stored in tracks adjacent to a selected track and to allow narrow track widths for high density data storage.
The read/write head is generally attached to an end of an actuator arm that is rotated across the disk to a selected track. As the head is rotated it becomes skewed relative to the tracks. To compensate for the skew angle the read element is sometimes displaced laterally from the write element.
The head is positioned by a head positioning system that causes the head to seek to a selected track and then precisely centers the head over the data stripe area in the track. Some positioning systems generate servo signals using servo information embedded within a portion of each track for determining the position of the head within a track. The head is centered over the servo information to align the head with the data. To compensate for the displacement between the read and write elements, the head is offset from the servo information to center the write element over the data stripe area for a write operation and to center the read element over the data for a read operation.
A limitation of many of these head positioning systems is that the head position signal becomes nonlinear as the narrow read element is offset from the servo information to the head position required for a read operation and/or a write operation. A nonlinear position signal reduces the accuracy with which the head can be positioned, causing a corresponding increase in the error rate for reading data. Consequently, there is a need for a head positioning system that accurately positions the head at all predetermined positions within all tracks.